Re: [PATCH] virtio-balloon: fix managed page counts when migrating pages between zones

[David Hildenbrand]

On 10.12.19 14:31, Michael S. Tsirkin wrote:
> On Wed, Dec 04, 2019 at 09:48:07PM +0100, David Hildenbrand wrote:
>> In case we have to migrate a ballon page to a newpage of another zone, the
>> managed page count of both zones is wrong. Paired with memory offlining
>> (which will adjust the managed page count), we can trigger kernel crashes
>> and all kinds of different symptoms.
>>
>> One way to reproduce:
>> 1. Start a QEMU guest with 4GB, no NUMA
>> 2. Hotplug a 1GB DIMM and only the memory to ZONE_NORMAL
>> 3. Inflate the balloon to 1GB
>> 4. Unplug the DIMM (be quick, otherwise unmovable data ends up on it)
>> 5. Observe /proc/zoneinfo
>>   Node 0, zone   Normal
>>     pages free     16810
>>           min      24848885473806
>>           low      18471592959183339
>>           high     36918337032892872
>>           spanned  262144
>>           present  262144
>>           managed  18446744073709533486
>> 6. Do anything that requires some memory (e.g., inflate the balloon some
>> more). The OOM goes crazy and the system crashes
>>   [  238.324946] Out of memory: Killed process 537 (login) total-vm:27584kB, anon-rss:860kB, file-rss:0kB, shmem-rss:00
>>   [  238.338585] systemd invoked oom-killer: gfp_mask=0x100cca(GFP_HIGHUSER_MOVABLE), order=0, oom_score_adj=0
>>   [  238.339420] CPU: 0 PID: 1 Comm: systemd Tainted: G      D W         5.4.0-next-20191204+ #75
>>   [  238.340139] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu4
>>   [  238.341121] Call Trace:
>>   [  238.341337]  dump_stack+0x8f/0xd0
>>   [  238.341630]  dump_header+0x61/0x5ea
>>   [  238.341942]  oom_kill_process.cold+0xb/0x10
>>   [  238.342299]  out_of_memory+0x24d/0x5a0
>>   [  238.342625]  __alloc_pages_slowpath+0xd12/0x1020
>>   [  238.343024]  __alloc_pages_nodemask+0x391/0x410
>>   [  238.343407]  pagecache_get_page+0xc3/0x3a0
>>   [  238.343757]  filemap_fault+0x804/0xc30
>>   [  238.344083]  ? ext4_filemap_fault+0x28/0x42
>>   [  238.344444]  ext4_filemap_fault+0x30/0x42
>>   [  238.344789]  __do_fault+0x37/0x1a0
>>   [  238.345087]  __handle_mm_fault+0x104d/0x1ab0
>>   [  238.345450]  handle_mm_fault+0x169/0x360
>>   [  238.345790]  do_user_addr_fault+0x20d/0x490
>>   [  238.346154]  do_page_fault+0x31/0x210
>>   [  238.346468]  async_page_fault+0x43/0x50
>>   [  238.346797] RIP: 0033:0x7f47eba4197e
>>   [  238.347110] Code: Bad RIP value.
>>   [  238.347387] RSP: 002b:00007ffd7c0c1890 EFLAGS: 00010293
>>   [  238.347834] RAX: 0000000000000002 RBX: 000055d196a20a20 RCX: 00007f47eba4197e
>>   [  238.348437] RDX: 0000000000000033 RSI: 00007ffd7c0c18c0 RDI: 0000000000000004
>>   [  238.349047] RBP: 00007ffd7c0c1c20 R08: 0000000000000000 R09: 0000000000000033
>>   [  238.349660] R10: 00000000ffffffff R11: 0000000000000293 R12: 0000000000000001
>>   [  238.350261] R13: ffffffffffffffff R14: 0000000000000000 R15: 00007ffd7c0c18c0
>>   [  238.350878] Mem-Info:
>>   [  238.351085] active_anon:3121 inactive_anon:51 isolated_anon:0
>>   [  238.351085]  active_file:12 inactive_file:7 isolated_file:0
>>   [  238.351085]  unevictable:0 dirty:0 writeback:0 unstable:0
>>   [  238.351085]  slab_reclaimable:5565 slab_unreclaimable:10170
>>   [  238.351085]  mapped:3 shmem:111 pagetables:155 bounce:0
>>   [  238.351085]  free:720717 free_pcp:2 free_cma:0
>>   [  238.353757] Node 0 active_anon:12484kB inactive_anon:204kB active_file:48kB inactive_file:28kB unevictable:0kB iss
>>   [  238.355979] Node 0 DMA free:11556kB min:36kB low:48kB high:60kB reserved_highatomic:0KB active_anon:152kB inactivB
>>   [  238.358345] lowmem_reserve[]: 0 2955 2884 2884 2884
>>   [  238.358761] Node 0 DMA32 free:2677864kB min:7004kB low:10028kB high:13052kB reserved_highatomic:0KB active_anon:0B
>>   [  238.361202] lowmem_reserve[]: 0 0 72057594037927865 72057594037927865 72057594037927865
>>   [  238.361888] Node 0 Normal free:193448kB min:99395541895224kB low:73886371836733356kB high:147673348131571488kB reB
>>   [  238.364765] lowmem_reserve[]: 0 0 0 0 0
>>   [  238.365101] Node 0 DMA: 7*4kB (U) 5*8kB (UE) 6*16kB (UME) 2*32kB (UM) 1*64kB (U) 2*128kB (UE) 3*256kB (UME) 2*512B
>>   [  238.366379] Node 0 DMA32: 0*4kB 1*8kB (U) 2*16kB (UM) 2*32kB (UM) 2*64kB (UM) 1*128kB (U) 1*256kB (U) 1*512kB (U)B
>>   [  238.367654] Node 0 Normal: 1985*4kB (UME) 1321*8kB (UME) 844*16kB (UME) 524*32kB (UME) 300*64kB (UME) 138*128kB (B
>>   [  238.369184] Node 0 hugepages_total=0 hugepages_free=0 hugepages_surp=0 hugepages_size=2048kB
>>   [  238.369915] 130 total pagecache pages
>>   [  238.370241] 0 pages in swap cache
>>   [  238.370533] Swap cache stats: add 0, delete 0, find 0/0
>>   [  238.370981] Free swap  = 0kB
>>   [  238.371239] Total swap = 0kB
>>   [  238.371488] 1048445 pages RAM
>>   [  238.371756] 0 pages HighMem/MovableOnly
>>   [  238.372090] 306992 pages reserved
>>   [  238.372376] 0 pages cma reserved
>>   [  238.372661] 0 pages hwpoisoned
>>
>> In another instance (older kernel), I was able to observe this
>> (negative page count :/):
>>   [  180.896971] Offlined Pages 32768
>>   [  182.667462] Offlined Pages 32768
>>   [  184.408117] Offlined Pages 32768
>>   [  186.026321] Offlined Pages 32768
>>   [  187.684861] Offlined Pages 32768
>>   [  189.227013] Offlined Pages 32768
>>   [  190.830303] Offlined Pages 32768
>>   [  190.833071] Built 1 zonelists, mobility grouping on.  Total pages: -36920272750453009
>>
>> In another instance (older kernel), I was no longer able to start any
>> process:
>>   [root@vm ~]# [  214.348068] Offlined Pages 32768
>>   [  215.973009] Offlined Pages 32768
>>   cat /proc/meminfo
>>   -bash: fork: Cannot allocate memory
>>   [root@vm ~]# cat /proc/meminfo
>>   -bash: fork: Cannot allocate memory
>>
>> Fix it by properly adjusting the managed page count when migrating. The
>> managed page count of the zones now looks after unplug of the DIMM
>> (and after deflating the balloon) just like before inflating the balloon
>> (and plugging+onlining the DIMM).
>>
>> Reported-by: Yumei Huang <yuhuang@xxxxxxxxxx>
>> Fixes: 3dcc0571cd64 ("mm: correctly update zone->managed_pages")
>> Cc: <stable@xxxxxxxxxxxxxxx> # v3.11+
>> Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx>
>> Cc: Jason Wang <jasowang@xxxxxxxxxx>
>> Cc: Jiang Liu <liuj97@xxxxxxxxx>
>> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>> Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
>> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
>> ---
>>  drivers/virtio/virtio_balloon.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
>> index 15b7f1d8c334..1089b07679cf 100644
>> --- a/drivers/virtio/virtio_balloon.c
>> +++ b/drivers/virtio/virtio_balloon.c
>> @@ -742,6 +742,12 @@ static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,
>>  
>>  	mutex_unlock(&vb->balloon_lock);
>>  
>> +	/* fixup the managed page count (esp. of the zone) */
>> +	if (!virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) {
> 
> That comment's isn't great ;) it repeats the obvious thing, but does

I don't think it's obvious that the zone is involved. Open for suggestions.

> not explain why it's done. Also, what does it have to do
> with VIRTIO_BALLOON_F_DEFLATE_ON_OOM?

As replied to Igor already, we only mess with the managed page count
when we don't have VIRTIO_BALLOON_F_DEFLATE_ON_OOM (check the other
callers in this file).

Please see v2 of this patch as well. Thanks


-- 
Thanks,

David / dhildenb